As the society is aging, there is an increasing demand for a caring robot for providing a nursing care instead of a human. Such a caring robot is required to have a tactile sense which is not inferior to that of the human skin so that the robot does not injure any human. A sensor provided in hands of the robot needs to sense a slip as well as a pressure.
Conventionally, for a tactile sensor for sensing a load, a piezo resistance type element is used. For example, Patent Document 1 discloses a technology by which a cantilever beam structure fixed on a substrate is covered with a soft elastomer part and a load applied to the elastomer part is sensed based on how the cantilever beam structure is deformed. According to this technology, a piezo resistance type element provided at a base part of the cantilever beam structure measures the distortion of the base part to sense the load applied to the elastomer part.
However, with this technology, the piezo resistance type element merely senses a stress applied to the cantilever beam structure statically. Therefore, merely with one cantilever beam structure, the direction in which the load is applied cannot be sensed although the magnitude of the load can be sensed. Hence, Patent Document 1 and Non-patent Document 1 each propose a technology of combining a plurality of cantilever beam structures to sense loads applied in different directions.
FIG. 7(a) is a perspective view showing a structure of a cantilever type tactile sensor unit 101 disclosed in Non-patent Document 1. FIG. 7(b) is a cross-sectional view showing the structure of the cantilever type tactile sensor unit 101. As shown in FIG. 7(a), the cantilever type tactile sensor unit 101 includes four cantilever beam structures 102 formed on a substrate 104, and the four cantilever beam structures 102 are covered with an elastomer part 103. Among the four cantilever beam structures 102, each two cantilever beam structures 102 located at positions opposite to each other face each other. As shown in FIG. 7(b), the cantilever beam structures 102 each include an Si layer 102a and a polymer layer 102b, and are each formed by curving the Si layer 102a and the polymer layer 102b toward the polymer layer 102b side.
FIG. 8(a) is a cross-sectional view showing a state where a normal load is applied to the elastomer part 103. FIG. 8(b) is a cross-sectional view showing a state where a shear load is applied to the elastomer part 103. As shown in FIG. 8(a), when the normal load is applied to the elastomer part 103, the two cantilever beam structures 102 are both deformed in such a direction that the Si layer 102a approaches the substrate 104. By contrast, as shown in FIG. 8(b), when the rightward shear load is applied to the elastomer part 103, the left cantilever beam structure 102 is deformed in such a direction that the Si layer 102a approaches the substrate 104, whereas the right cantilever beam structure 102 is deformed in such a direction that the Si layer 102a is distanced away from the substrate 104. The cantilever beam structures 102 have a resistance changing in accordance with the deformation. Therefore, based on a change in the resistance of each cantilever beam structure 102 at the time of deformation, a normal directional component of the load applied to the elastomer part 103 and a shear directional component of the load applied to the elastomer part 103 can be sensed separately.